1. Field of the Invention
The present invention relates to a cation exchange membrane of a fluorinated polymer for an electrolysis of an alkali metal chloride which has excellent electrolytic characteristic and mechanical characteristics and an electrolysis of an aqueous solution of an alkali metal chloride using the membrane.
2. Description of the Prior Arts
It has been known to produce chlorine in an anode compartment and alkali metal hydroxide in a cathode compartment by partitioning the anode compartment and the cathode compartment with a diaphragm and feeding an aqueous solution of an alkali metal chloride into the anode compartment to electrolyze it. The method has been known as a two-compartment type diaphragm electrolysis.
Recently, it has been proposed to use a cation exchange membrane of fluorinated polymer which does not substantially pass the electrolyte and selectively pass only alkali metal ions and has high alkali resistance and chlorine resistance.
When such cation exchange membrane is used as the membrane, the electrolyte is not substantially passed through the membrane, but only alkali metal ions are selectively passed whereby the contamination of an alkali metal chloride in an alkali metal hydroxide can be prevented to obtain a product having a satisfactory purity.
However, the current efficiency has not been satisfactory, when the conventional cationic exchange membrane of a fluorinated polymer is used. It has been proposed to give excellent electric characteristics of the increase of the current efficiency in the electrolysis and the remarkable decreases of the electrolytic voltage of an alkali metal chloride by using a cationic exchange membrane of a carboxylic acid type fluorinated polymer having--COOM (M represents a hydrogen atom or an alkali metal atom) as ion exchange group.
When such cation exchange membrane of the carboxylic acid type fluorinated polymer is used for the electrolysis of an aqueous solution of an alkali metal chloride, the electrolytic characteristics are excellent, however wrinkle are easily caused in the membrane during the electrolysis. The gas formed in the electrolysis is stayed at the parts of the wrinkle to increase the cell voltage. When the membrane is used for a long period, the deterioration of the tissue of the membrane is caused. The membrane is contacted with the net type electrode by the wrinkle so as to cause a damage of the membrane, sometimes.
The ununiform flow of the electrolyte is caused in the electrode compartments by the wrinkle. In such cases, the concentration of the alkali metal chloride is partially decreased and the flow resistance of the solution is increased and the current efficiency is decreased as the troubles.
The inventors have studied to overcome various troubles caused by the formation of the wrinkle in the cation exchange membrane of the carboxylic acid type fluorinated polymer.